The present invention relates generally to compliant hinges used in deployable or reconfigurable mechanisms, and in particular to hinges that connects three or more struts, allows struts to translate and rotate finite amounts relative to each other, has increased compliance during deployment, and is locked out in a strong and stiff manner in its deployed configuration. A four strut version of the compliant hinge disclosed herein is the type of hinge required in a pending patent application Ser. No. 12/555,034, “Deployable Structures with Quadrilateral Reticulations.”
In deployable or reconfigurable mechanisms, structural members must move relative to each other to accommodate folding. In many situations, the kinematics of the mechanism are such that pin-clevis joints provide sufficient relative motion. A good example of this is the SquareRigger structure disclosed in U.S. Pat. No. 7,211,722. In this structure, articulation of the hinges is sufficient to deploy the structure without deformation of any members. In other words, the structure could be composed of rigid elements connected by pin-clevis joints and no internal stresses are generated during deployment. This class of mechanism is said to be compatible throughout its deployment, i.e., the member lengths and hinge locations are “compatible” with a stress free structural configuration. A problem associated with this class of structure is binding. Any strut or hinge length or alignment error generates internal loads in the mechanism, resulting in increased friction in the pin-clevis joints. Joint friction can cause these structures to bind and prevent deployment.
Structures that are not compatible throughout deployment generate internal loads and some compliance is required to prevent excessive loads from building up. These structures also need to be strong and stiff in the deployed configuration so that reducing the stiffness (adding compliance) to the struts results in a reduced stiffness deployed structure. What is needed is a hinge mechanism to render non-compatible structures deployable that behaves similar to a pin-clevis hinge, but has increased compliance during deployment and is locked out in a strong and stiff manner in the deployed configuration. A recognized hinge design demonstrating these characteristics is known as strain energy or tape measure hinge. The hinge bends about a single axis allowing the hinge to fold such that the once opposing ends are adjacent. Hinges of this type have been used on existing deployable structures. In applications requiring folding in multiple axes at a single location, such as in umbrella-type structures described in U.S. Pat. No. 7,009,578, multiple single-axis tape measure joints are connected to a central hub structure. The disadvantages of this type of joint include the increased mass and packaging dimensions due to the central hub.